I've not trained under Andy Cullen, but certainly heard the name. Sounds like you're on the right path. To be honest, I found the gun dog stuff I've done has done more for my dogs' general "obedience" (although I hate that term) than anything else I could ever have done. I don't get to classes often, because of geography, and will never be a regular on a shoot for the same reason, but we all really enjoy the training. A sit for a sit's sake is boring. A sit to line up for a retrieve is hugely exciting!